1. Field of the Invention
The invention relates to water-redispersible polymer powder compositions with accelerated-setting action, to a process for their preparation, and to the use of these powders in hydraulically setting systems.
2. Background Art
Polymers based on vinyl esters, vinyl chloride, (meth)acrylate monomers, styrene, butadiene, and ethylene are used in a wide variety of applications, especially in the form of their aqueous dispersions or water-redispersible polymer powders, for example as coating compositions or adhesives for a very wide variety of substrates. Protective colloids or low-molecular-weight surface-active compounds are used to stabilize these polymers. The protective colloids generally used comprise polyvinyl alcohols.
These products are in particular used as binders in hydraulically setting adhesives, for example in tile adhesives based on cements or calcium sulfates.
Concrete is a very versatile material whose properties can be controlled via numerous parameters. Important properties are, inter alia, workability as a function of time and strength (early strength and final strength) of the concrete. Workability reduces with time as the hydration of the material proceeds. On account of this effect it is possible to add either more water or “superplasticizers”. However, both have an adverse effect on the initial and final strength of the concrete. To compensate for these disadvantages, “accelerators” or materials which promote early strength are added, these leading to higher initial and final strength.
EP-A 1136507 describes tertiary alkanolamines as accelerators long known to those skilled in the art. A disadvantage is that these compounds are highly active nucleophiles and therefore hydrolyze the ester groups in the polymer-containing binders generally used, which are based on vinyl acetate-ethylene copolymers or on styrene-acrylate copolymers, and degrade the effectiveness of the binders as well. In EP-A 1136507 the alkanolamines are therefore linked by a complicated method to a polymer skeleton.
EP-A 1167317 relates to water-soluble, fluoride-containing or sulfate-containing aluminum salts as accelerators for setting and hardening.